Removal of Pb(II) from Aqueous Solution by Acrylic Acid Modified Walnut Shell: Isotherms and Kinetics

The adsorption isotherms and kinetics of acrylic acid modified walnut shell (AA-WNS) for Pb(II) were investigated in the temperature range of 288-308K. Scanning electron microscope (SEM) was utilized for evaluation of the developed walnut shell. Adsorption isotherm data were better interpreted by Langmuir isotherm model, and the maximal adsorption capacity was 238.65 mg g-1 at 308 K. The adsorption kinetic data were well correlated by pseudo-second-order model. The adsorption process was governed by both film and intraparticle diffusion, with film diffusion at the fast stage followed by intraparticle diffusion. A Boyd kinetic plot confirms that the slowest step of Pb(II) adsorption by AA-WNS is film diffusion. The thermodynamic parameters ∆G, ∆H and ∆S were determined. Recycling properties of AA-WNS were studied, indicating that it can be reused for Pb(II) adsorption.